1. Field of the Invention
This invention relates to a resistance change memory device, specifically to a write buffer circuit used therein, with which cell's data state transition may be stabilized.
2. Description of the Related Art
A resistance change memory (i.e., resistive RAM; ReRAM), in which the resistance state of cells is exchanged by voltage, current or heat and it serves as data, is noticed for succeeding the conventional NAND type flash memory. The ReRAM is suitable for shrinking the cell size and for constituting a cross-point cell array, and the cell arrays may be easily stacked. Therefore, it is noticed that a large capacity of file memory may be constructed with a three-dimensional cell array (for example, refer to JP2009-009657A).
One of the features of an ReRAM cell is in that a state change operation from a high resistance state to a low resistance state and the other state change operation from the low resistance state to the high resistance state are different from each other in these electrical conditions. Explaining in detail, for example, the former is characterized as a “voltage operation” while the latter is characterized as a “current operation”.
Further, one data transition may be performed with voltage application at a high speed while it takes a long time with current application for performing the other data transition. To keep the cell's state stable after state transition, the circuit load becomes too large. Additionally, in a highly integrated cell array, the influence of the parasitic resistance and capacitance becomes different in accordance with the cell position on a wiring line, so that it becomes difficult to write data with a sufficient margin.